APL and the VT FUZE

The inexorable movement of the signals then interact to create a United States toward entry into "ripple" signal which is amplified World War II gave great urgency, in by vacuum tubes. When the pro­ 1940, to the search for new weapons jectile comes within a radius of about with which to combat a massive 70 feet from the target, the ripple enemy air threat. Among many such pattern becomes strong enough to weapons long envisioned was the trigger the thyratron tube that serves proximity fuze- a mechanism for as a switch. That action releases the detonating an explosive shell within electrical energy in a charged con­ kill range of an aircraft. While this denser, and the current, in turn, had long been considered impossible initiates an explosion in the electrical to attain, a project was nevertheless detonator, or squib. That blast launched in mid-August 1940, to activates the standard electrical investigate three possible mechanisms detonating fuze which sets off the for this type of fuze: photoelectric, main explosive charge in the pro­ acoustic, and radio. jectile. If the triggering pattern of the fuze coincided with the fragmentation Fuze Program Begins pattern of the shell, a "kill" was On June 27, 1940, the National probable .. . . In completed form, the Defense Research Committee had VT fuze consisted of four principal been founded, with Dr. Vannevar parts: A radio frequency oscillator and Bush as its chairman, to serve as a receiver, an amplifier and thyratron functioning link between the National tubes, a battery, and an explosive Academy of Science and the military train incorporating vital safety fea­ tures."l services. This organization, comprised of eminent scientists and educational Paralleling the scientific effort in leaders, was divided into divisions, of developing the so-called VT fuze, which Division A was to give its the organization supporting the work attention to problem,; of armor and was growing apace. Early work, with ordnance. Division A was further a handful of scientists, was done at the Carnegie Institution Department broken down into working teams, or Cutaway view of a typical VT fuze. sections, which would investigate of Terrestrial Magnetism. When the proximity fuze had emerged from the certain well-defined problems. One 1942, a production contract for a "impossible" category and was firmly of these had assigned to it the search basic model of the fuze, for Navy seated in the "probable," the need for for a proximity fuze; this was Section 5-in. guns, could be written. more space became desperate. In T, with Dr. Merle A. Tuve as its The VT (variable time), or consequence, all of Section T's work chairman (each section was known by proximity, fuze is clearly described by on projects other than the shell fuze its chairman's initial). At the time the Bureau of Ordnance: the con­ was removed physically and organiza­ of his appointment on Aug. 24, 1940, figuration selected as most promising tionally to the Bureau of Standards. Dr. Tuve was a member of the staff for anti-aircraft use was one "in of the Department of Terrestrial which the transmitter and receiver Founding of APL Magnetism of the Carnegie Institu­ were both located on the projectile. tion in Washington, D. C. This ... self-contained unit functions This move proved to be only temporary relief, however, with the From August 1940, until early in by transmitting a continuous pattern 1942, the radio shell fuze moved at a of [radio] waves in space. These ultimate result that on Mar. 10, 1942, fast pace through the phases of idea signals are reflected back to the a contract was signed by the Office of conception, search for components, oscillator by any target that gives a Scientific Research and Development testing, redesign, firing tests, and radio reflection. At first the pro­ and The Johns Hopkins University organizational growth in both jectile is so far from the enemy that which stipulated that the University numbers of personnel and the size of the signals are not returned with any would furnish laboratory space, facilities required. By Sept. 1941, after strength. As the projectile nears the equipment, test site, and additional frenzied effort, a complete fuze had target, however, the reflected waves 1 B. Rowland and W. B . Boyd, " U. S. Navy functioned properly at the end of its picked up by the oscillator grow Bureau of Ordnance in World War II," U. S. trajectory in a test firing. By Jan. stronger. The outgoing and incoming Government Printing Office, 1953, 278-279 .

18 APL Technical Digest personnel for furthering the VT fuze at the Silver Spring location. were tested under all conceivable program. Dr. Tuve was to continue The pressure for still more space operating conditions for all sizes of as head of the program, and overall continued, however. The rapidly guns for which radio fuzes were to be administration was transferred to the expanding program seemed always to produced, as well a3 for various OSRD. Dr. Tuve conceived the name be exasperatingly ahead of the avail­ changes in design intended to correct "Applied Physics Laboratory" for able physical facilities. In spite of a previous test failures. The search for the new organization operating under new building constructed just north of glass rugged enough to withstand the The Johns Hopkins University. the garage, plus two new floors added shock of gunfire was constant, as it With this brief background of the to the original building, and a new was for filaments, bridge wire, and emergence of the VT fuze, we may connecting building, the space avail­ wax. Even after the fuzes were in now look in some detail at the vastness able for the Laboratory's work never production, the test program ob­ of the fuze program and at its impact seemed to be adequate. jectives persisted in the quality control on the unfolding drama of World Needed facilities other than space program. War II*. to house the Laboratory included a Illustrative of the experience that The Johns Hopkins University new test field equipped with shelters supported the need for the continual entered upon its new responsibilities for the personnel conducting tests, program of testing, even through in a manner that gave promise of machine tools, instruments of various quantity production, is Dr. Tuve's continued rapid progress in the kinds, and other related equipment for summarization of the development of development of the VT fuze. The laboratory and field use. A suitable rugged tubes: President of the University appointed site at Newtown Neck, Md., was leased "Empirical factors enter in other ways D. Luke Hopkins, member of the and equipped for the safe conduct of than performance. For example, some Board of Trustees, as the official vertical recovery firings. design factors unpredictably limit representative of the University in all In spite of the many details that production. We started five companies matters pertaining to APL. Mr. had to be taken care of in the reloca­ on the design and manufacture of Hopkins stated that the University's tion to Silver Spring, and the establish­ rugged tubes, during 1940 to 1942. purpose was "to see to it that the job ment of new administrative and All designs were successfully rugged progressed as smoothly, expeditiously, communications channels, these tasks and made into successful fuzes. One and efficiently as possible." were accomplished in good time. The failed to make them on anything but The immediate task, of course, was increase in staff from 100 in 1942 to a laboratory basis, although large to provide whatever was most needed 700 in 1944, under difficult con­ amounts of money were spent on to enable Section T's expanding ditions imposed by the need for pilot production lines during two program to be carried on effectively complete secrecy, probably could years. The second has made rugged by the newly established Applied never have been done under the tubes continuously since early 1941. Physics Laboratory. The most im­ restrictions that had existed before Maximum production ever reached portant and most obvious requirement the entrance of The Johns Hopkins was 4000 per day, with limited use was additional personnel, but before University in the role of contractor­ of these tubes as substitutes. The third new staff could be taken on, office operator for the OSRD. company started 1940 with fairly and shop space adequate to ac­ successful tubes, kept in production commodate them had to be acquired. Problems of Design to early 1944, but could never exceed In Silver Spring, Md., a sparsely Recalling Dr. Tuve's statement 20,000 per day because the design settled cross-roads community at the that the success of this type of fuze was was not adapted to fast produc­ time, a garage was found which, it dependent on a great number of tion .... The fourth company is now appeared, would serve well for the empirical factors, each dependent our primary supplier (260,000 per present at least. upon design of specific components, day). The fifth company made two Lease of this property, 861 7 to we can appreciate the need for the million tubes, but characteristics 8621 Georgia Ave., was arranged by continuing program of testing. This were poor and fuzes variable. The the University to include not only the included complete fuzes as well as tubes were set aside and production garage floor but also the second and tubes, oscillator circuits, detonators, stopped early in 1943. (The sixth third floors which were then occupied explosive charges, and other com­ company was started and factory by a Social Security office. Many ponents. Among the latter were the built but the factory was turned over problems in adapting this building safety switches to prevent the shell to other work at our request.)"2 for use by the new Laboratory were from exploding either in the bore of a overcome in a short time in spite of gun or within 0.3 to 0.5 sec after Mass Production Begins wartime limitations on materials leaving the muzzle, and self-destruc­ As the first of the production fuzes and a tight labor market. The date of tion mechanisms designed to explode became available, the need for May 1, 1942, may be considered to the shell after it had passed beyond carrying the test program still farther mark the start of operations by APL the target. The self-destruction feature was recognized. Until that time, was incorporated to prevent friendly • These historical notes are adapted from a units near the line-of-fire-extended 2 Letter from M. A. Tuve to Lt. Col. C. F. Fell, history of the Applied Physics Laboratory from being endangered and enemy Army Member of JPS Subcommittee; subject, being prepared under the direction of Rear "Confirmation of Important Features in De­ Admiral M. R. Kelley, U . S. Navy (Ret.), as­ forces from having an opportunity to velopment and Production of VT Fuze," sisted by staff members of APL. recover a dud. These components Sept. 28, 1944.

September-October 1962 19 operation of the fuze test samples had circuit so that it could not be fired. been checked only by firings in which The wall of the inner chamber was a the radio waves that triggered the diaphragm of relatively porous fuze were reflected from the water as material through which the mercury the shell returned to the surface on could pass under centrifugal force the downward leg of its trajectory. A generated by the post-firing spin of the test that more accurately represented projectile, thereby removing the short a shell approaching an aircraft was in the primer circuit. The purest obviously needed. This was done for mercury obtainable commercially was the first time at Parris Island in procured for this use, but it was April 1942, when a full-scale aircraft nevertheless subjected to additional target suspended from a balloon distillation before it was considered triggered the fuze. Later, chicken to have the required purity. Selected wire replicas of full-scale aircraft samples of the thousands of switches were suspended between two towers, manufactured daily were then spun and test fuzes were fired at them for at a rate to produce the centrifugal determination of operational per­ force resulting from the projectile formance. Tests of production fuzes spin after firing. The time required Colonel H. S. Morton and Drs. L. R. Hafstad for the mercury to pass through the were then conducted against drone and M. A. Tuve (1. to r.) examine early VT targets in Chesapeake Bay from the diaphragm was accurately determined fuzes for use in Europe. USS Cleveland. The three drones and, for acceptance, had to lie within allotted to this series of tests were specified limits. Rough handling With quantity production of a fuze destroyed on the first day of firing by tests of the switches followed, with for the Navy's 5-in. guns getting four proximity bursts. Because of this each checked by X-ray to insure that underway in the fall of 1942, a very success, these realistic tests were it met the prescribed standards. Under urgent problem which had already considered a final " dress rehearsal" a regime of such supervision and been recognized came to the fore. for the shell radio fuze before its first testing it is easy to see why safety This was the need for appropriate appearance in a theater of combat. provisions proved so successful. steps to be taken to indoctrinate the From these results, specifications for combat forces in its proper handling Military Demands a quantity production fuze were and use. A necessary follow-on of crystallized and production began. In the spring of 1941 , priontles utmost importance was to build up had been established to meet require­ their confidence in its capabilities so High Priority of Safety ments of the armed forces in the that they would overlook no oppor­ For the many models of the shell following order : U. S. Navy, British tunity to use it in action. Once they radio fuze that were manufactured Navy, U. S. Army, and British had seen results, it was felt by those and/or tested, exceptional care was Army. Because of the optimism that who were engaged in the develop­ taken to safeguard personnel against had grown in the Section T program, ment and test program, and by those bursts in handling or in the bore of the the U. S. Joint Chiefs of Staff con­ of the Navy who had followed this gun, and to insure delay in postfire sidered the matter of time and place program closely, that the users would arming. The standard of safety set up of introducing the fuze into the be enthusiastic. as a requirement was no more than various areas of combat operations. The proximity fuze did not present one muzzle burst in a million rounds. The above priorities reflected the the kind of breakthrough that would Not only in the design of the safety viewpoint of the Joint Chiefs in their at once demand a change in either and arming element was such care concern lest the fuze fall into enemy the strategy or tactics of the allied taken, but also in the inspection and hands shortly after its initial use in forces. Rather, it gave promise that test program. An example will show combat. This would have made it pos­ the strategic plans already in effect, the painstaking care used to preven t sible for the Axis powers to develop and the tactics being employed, accidental bursts. The mercury un­ counter-measures to reduce the effec­ could be confidently adhered to shorter switch was designed to pre­ tiveness of the fuze and/or to develop with the expectation of a decisive vent operation of the fuze during their own versions of the fuze. If either victory. Without the new fuze, on the handling and loading and to insure had resulted, the advantage to the Allies other hand, revision of both strategy that the shell could not be exploded of sole possession and use of this new and tactics at the appropriate levels until it had traveled a certain distance weapon would have been substantially might be forced upon the Allies from the muzzle. It was cylindrical reduced. Aside from the fact that the because of their losses to attacking in shape, slightly over 0.25 in. in U. S. Navy had assigned the highest aircraft and the German V born bs. diameter, and about 0.4 in. long. priority to the shell radio fuze and Experienced officers in the Navy Inside an outer chamber or sump, was supporting its development in Bureau of Ordnance who had close which was empty prior to high-speed every possible way, there was, of contact with the fuze program were spin of ·the projectile, was an inner course, the obvious fact that use of the quick to see that indoctrination of the chamber filled with mercury. In this fuze by naval forces afloat would fighting forces in its capabilities and location the mercury maintained an greatly reduce the likelihood of its use was of utmost importance if the electric short in the cannon-primer being recovered by the enemy. full benefits of this new weapon were

20 APL Technical Digest to be reaped quickly. And Dr. Tuve's made such an important contribution into the Atlantic and Mediterranean instruction on the subject of Section to total Allied victory. areas would be greatly aided by this T's moral responsibility would clearly experience, especially if its safety indicate what importance he attached The Problem. of the Fuze in and performance record proved to be Europe to such indoctrination. all that was desired. In addition to the three APL The Navy'S indoctrination team The Fuze Goes into Action scientists commissioned to assist in arrived in the Mediterranean in the Since the Combined Chiefs of introducing the new fuze to Pacific closing days of the North African Staff felt strongly that the fuze should Fleet units, two other APL staff campaign and had completed intro­ not be used where a dud might be members had been selected for the ductory instruction for all concerned recovered on the ground, the South same duties in the Atlantic and by the time the Sicilian operations Pacific, where Japanese land-based Mediterranean areas: Lieutenants E. got under way. Confidence in the new aircraft were a constant and serious R. Chatham and R. Morison. But fuze was more easily built up because menace, seemed the area of first introduction of the fuze in these areas action reports from the Pacific were importance. First deliveries of the new was intentionally delayed about six available to bear out the claims of fuzes, then, were to be made to ships months for several important reasons. the instruction teams. in that area having the 5-in. guns for First, the waters in which the Pacific On the Army side, a well-planned which the earliest production fuzes Fleet units were operating were of program of indoctrination was put were designed. During October 1942, appreciably broader expanse and into effect. Colonel H. S. Morton, 500 fuzes for shipboard use were were much less likely to be monitored assigned as the Army's liaison officer produced each day and shipped by high-performance radio counter­ to Sections T and E, and later to immediately to the Naval Ammuni­ measures and direction-finding equip­ APL, was a key figure in this pro­ tion Depot, Mare Island, where they ment at strategic points on land. gram. As early as Sept. 1942, the were inserted in the fuze cavities of It was thought that the Germans Army had asked for 1,000,000 prox­ 5-in. shells. Of each day's consign­ would be much more likely than the imity fuzes. Accompanied by transfer ment, 10 % were withdrawn and flown Japanese to have such equipment, of the necessary funds to support the back to the Naval Proving Ground, and at this stage of the war would no stated requirement, this indication of Dahlgren, Va., for test. When 5000 doubt have the vital sea areas well faith in the project was of vital proximity-fuzed projectiles had ac­ monitored. Another factor was that importance to its continued progress, cumulated, Commander W. S. injection of the fuze into combat especially when the Army's primary Parsons, Special Assistant to the situations on a broad scale would effort and financial support had been Director, OSRD, went to Mare require time in which to check out directed to the photoelectric fuze Island to supervise loading of the battery personnel, tactics, fuze per­ project of Section E. shells for air transportation to Pearl formance under shipboard conditions, Colonel Morton was sent to Europe Harbor. He then flew to Hawaii, and indications of enemy jamming. where, from the beginning, he talked leaving the ammunition in the care of Early experience gained in the Pacific about the proximity fuze to any and three scientists from APL specifically could be used to modify defects in the all officers who would listen to him. commissioned for this duty: Lieu­ fuze, develop the most effective Those in the highest command tenants N. E. Dilley, R. P. Petersen, tactics for its use, and check out echelons, as well as officers in the and J. A. Van Allen. logistics and handling problems. lower echelons who would have the Successful introduction of the fuze responsibility for using the fuzes in First Strike-Pacific Theater battle, were given thorough briefings At Pearl Harbor the shells were on it and on the advantages it offered loaded into the aircraft tender USS for use against both ground and air Wright for transshipment to Noumea, targets. Some of them, of course, New Caledonia, where Commander already knew about the fuze, and Parsons reported to Admiral Halsey. some undoubtedly felt that this was a Three ships of the Third Fleet re­ new "gimmick" that might be worth ceived portions of this first shipment­ a try. USS Enterprise, USS Saratoga, and Colonel Morton outlined the most USS Helena- and indoctrination of effective methods of employment over their personnel commenced immedi­ different kinds of terrain and against ately. There was a period of relative low- and high-altitude air attack; inactivity in the Third Fleet area at also, the dangers involved for U. S. the time, extending into the early observation aircraft engaged in spot­ months of 1943, an excellent time for ting artillery fire. F or the field indoctrination but giving little op­ artillerymen especially, the fuze portunity for battle test of the new promized to be an ideal solution to fuze. On Jan. 5, 1943, however, a the problem of putting bursts at an Japanese plane was destroyed by a optimum altitude above the ground proximity fuze, the first of a long when used against personnel and other record of encouraging successes that The VT fuze on Iwo Jima in 1945. battlefield targets.

September-October 1962 21 designed to "play" for a few moments! Feeding these assembly plants (Crosley, Sylvania, RCA, Eastman Kodak, McQuay-Norris) were a host of more than 2000 interlocking suppliers and subsuppliers. The Sylvania Company, with 23 plants in the eastern part of the United States, supplied over 400,000 tubes per day; the National Carbon Company, with a major plant at Winston-Salem, North Carolina, con­ structed especially for T, and the A pattern of bursts of VT -fuzed anti-personnel shells over a battlefield in France during Eastman Kodak and Hoover World War II. Companies were turning out one APL Keeps Pace with Changing handling and loading equipment, and tenth of a million batteries a day."3 Demands of course in the basic missions for Production Miracle Reviewed As a build-up for indoctrinating which each was designed. the fighting forces in use of the fuze, A measure of these complexities In view of the many complexities Dr. Tuve had seen early the desir­ is obtained when we note that there of the program, the actual production ability of instructing Army and Navy were eight models of the shell radio of proximity fuzes assumed the status personnel in the design, inspection, fuze required for the U. S. Navy, of a miracle, as a few figures will handling, and functioning of proximity four for the British Navy, twelve for indicate. Assembly of production fuzes. This was in line with his views the U. S. Army, and six models for the fuzes began in Sept. 1942 and that the fuze must be closely followed British Army. The modifications that averaged 500 a day during the by APL right to the field of battle. were needed introduced some fears first month. A little more than a year The Ordnance Department of the that a modified fuze might prove later (Dec. 1943), 1,164,000 fuzes Army, fully appreciating the im­ unsafe in its handling, loading, and had been produced for the Navy and portance of a program to introduce firing cycle; hence, the seemingiy 126,000 for the Army. During 1944, the fuzes to appropriate Army units, endless program of testing this one a total of 8,301,000 fuzes were pro­ selected 200 officers and men for feature continued to demand the duced. By the end of that year, more training at APL and at the Bureau greatest care. As if these problems than 40,000 proximity fuzes per day of Standards. These men participated were not complicated enough, many were coming from the assembly lines. in certain phases of the development planners and operators in the using Altogether, 22,073,481 fuzes were work at the laboratories and in field services were changing their minds produced up to Aug. 14, 1945. testing, as well as in those methods of at frequent and unpredictable inter­ The development and manu­ handling the fuzes that were pertinent vals concerning the number of fuzes facture of proximity fuzes was one of to battlefield operations. The Navy of each model they would need. the best-kept secrets of the war. For also selected officers and men for The Applied Physics Laboratory reasons already given, it is well that advanced training in the shell radio was not, of course, in the business of this was the case. The success with fuze at APL. The trainees of both producing these different types of which the secret was kept seems no Services contributed in no small fuze. However, APL had the principal less a miracle than the production degree to the success of the entire responsibility for the design adapta­ miracle, in view of the fact that an program. tions, a responsibility which certainly estimated one million persons par­ With the start of quantity produc­ could not be dropped at the moment ticipated in the research, develop­ tion in the fall of 1942, many complica­ the modified fuzes were put into ment, and production of the fuze in tions arose, resulting in part from the production. Without full cooperation the United States, and in its use in priorities established by the Com­ of the many industrial contractors combat. The extraordinary pre­ bined Chiefs of Staff. Many diverse under Section T, this responsibility cautions taken to insure this secret requirements had to be satisfied could not have been discharged. are a fascinating story in themselves. within a time scale that would permit The extent of the industrial par­ As stated by Admiral Ernest J. each of the military forces to bring ticipation in the program has been King, then Commander in Chief of its full weight to bear in execution of succinctly summarized in the official the U. S. Fleet, "the development of the overall strategic plan. The basic history of the OSRD as follows: the VT fuze was a major scientific design of the proximity fuze for the "In the months just preceding V-J achievement that has contributed Navy'S 5-in. guns could not, merely Day (there was no slackening in the greatly toward winning the war for by a process of rescaling the dimen­ work of "T" after V-E Day) the the United Nations." sions, be readily adapted for use in Central Laboratory at Silver Spring the vario"lis types of guns in the other was the nerve center of a vast, country­ 3 "New Weapons for Air Warfare," ed. by J . C. three military organizations. There wide activity. Five major plants were Boyce; Little, Brown and Co., Boston, 1947, 172. This is one of a series of volumes of the were differences in caliber, muzzle rolling out some 70,000 VT-Fuzes a official history of the Office of Scientific Re­ velocity, rate of projectile spin, day-millions of tiny radio sets search and Development.

22 APL Technical Digest